Metal ion recovery system

ABSTRACT

A metal ion recovery system first removes most of the plating solution from recently plated articles in a relatively concentrated form and removes the remainder of the solution in much less concentrated form. These solutions are treated separately with only the lower concentrated solution being completely deionized to remove said metal ions therefrom.

United States Patent Zievers etal.

[451 Apr. 25, 1972 METAL ION RECOVERY SYSTEM Inventors: James F. Zievers; Clay W. Riley; Richard W. Crain, all of La Orange, 111.

Assignee: Industrial Filter & Pump Mfg. Co.,

Cicero, 111.

Filed: June 16, 1969 Appl. No.: 833,312

US. Cl. ..23/l45, 23/87 R, 23/97, 23/117, 23/125, 75/101 BE, 75/117, 75/119,

Int. Cl. ..B01k 3/00, C23b 5/06, COlg 37/02 Field of Search ..204/232, 237, 275, 51, 49, 204/52; 210/37, 38; 75/121, 119, 117, 101 BE; 117/130 E; 23/145, 87 11,97,117, 125

USED CATION REGENERANT [56] References Cited UNITED STATES PATENTS 3,542,651 1 H1970 Yagishita ..204/237 X OTHER PUBLICATIONS R. J. Rominski et al., Proc. Am. Electroplaters' Soc., Vol. 38, pp. 37-48, 1951).

J. M. Culotta eta1., Plating, pp. 25 l- 255, March 1970 C. F. Paulson et al., Plating, pp. 1,005- 1,009, Sept. 1953.

Primary ExaminerG. L. Kaplan Art0rneyFidler, Bradley, Patnaude & Lazo [5 7] ABSTRACT A metal ion recovery system first removes most of the plating solution from recently plated articles in a relatively concentrated form and removes the remainder of the solution in much less concentrated form. These solutions are treated separately with only the lower concentrated solution being completely deionized to remove said metal ions therefrom.

9 Claims, 1 Drawing Figure RINSE PLATING BATH HOLDING TANK HOLDING TANK Z2.

METAL ION RECOVERY SYSTEM The present invention relates to a method and system for recovering metal from a metal plating solution carried from a metal plating bath by the articles being plated.

In the operation of a continuous or conveyor type plating system, a substantial amount of .metal in solution is carried from the plating bath by the conveyor and the articles being plated. Because the amount of the unused plating solution which is thus carried out of the plating bath is substantial, it is economical to recover it. Even were it not economical, however, it would still be necessary to remove certain of the materials such as chromium, nickel, copper, ca'dmium, tin, zinc, gold, silver and the like, before discharging the solution into streams and the like to prevent pollution. Since the plating solution normally becomes contaminated by the articles being plated as well as by impurities carried by the articles into the bath, it is the usual practice to remove such contaminants from the recovered plating solution before it is returned to the plating bath.

In the past, the plating solution carried out of the plating bath has been recovered in one of three different ways. In one of these the articles and the conveyor'are thoroughly washed with a substantial quantity of water resulting in a large volume of solution, having an extremely low concentration of the plating metal ions. Very large anion and/or cation exchangers are used to remove the contaminants and recover the desired metal ions. During regeneration the desired metal ions are plating baths, the hexavalent chromium in the solution carried.

from the plating bath is reduced to trivalent chromium which precipitates out of the solution to form a sludge which must be removed from the settling tanks and transported to a suitable site where pollution will present no immediate problem.

The method and system of the present invention is superior to all three of these systems in that it provides a practical and more economical method of recovering and purifying the metal plating solution carried from the plating bath.

Briefly, the present method and system for recovering metal ions from a metal plating solution carried from theplating bath by the articles being plated consists of first subjecting the recently plated articles to a fog or spray rinse to remove the major portion of the plating solution therefrom while main taining the thus removed solution in fairly concentrated form, then rinsing the articles in deionized water to remove the remainder of the plating solution therefrom-in a much lower concentration, deionizing only the less concentrated solution by treatment with a cation resin and an anion resin and using the deionized liquid resulting therefrom for rinsing the articles. ln recovering metals in the form of negative ions, the

anion resin is first regenerated to remove the negative ions I therefrom and the used regenerant (effluent) is then passed through the cation resin and mixed with said fairly concentrated solution. The cation resin is then regenerated and thereafter the mixed solution is passed therethrough and into an evaporator where its concentration is increased to a level suitable for return to the original plating solution. In recovering positive metallic ions the cation resin is first regenerated with acid and the effluent is then passed to the evaporator where its concentration is increased to a levelsuitable for return to the original plating solution.

Referring now to the drawing wherein is shown a system for recovering chromium, the articles to be plated (not shown) are carried by a conveyor in a direction from right to left successively into and out of the adjacent tanks 1 through 7, inclusive. The articles are first passed through a rinse tank 1 and thence into a rinse tank 2 from which they are carried into the plating tank 3. Rinse water flows into the tank 2 and across a weir into the tank 1 and thence out of the system. This rinse is conventional and is used to remove surface impurities from the articles. The tank 3 contains a suitable plating solution which may have a concentration of chromatic acid, H CrO of about 30 percent or more. The exact formulation of the plating bath varies since each supplier has its own formula which in accordance with the normal practice of the industry is maintained as a trade secret. In addition to the chromic acid, however, the plating baths will ordinarily include a small percentage of sulfates, fluorides, and organic brighteners.

After being plated the articles are carried from the tank 3 into a fog rinse tank 4 wherein deionized water in the form of a very fine spray or fog is directed onto the articles from a plurality of fog nozzles 8 suitably located in the tank 4. Under normal conditions, approximately percent of the plating solution is removed from the articles in the tank 4 and is fed to a holding tank 10. The solution which is thus supplied to the holding tank 10 has a concentration of chromic acid in the range of about 2 to 4 percent. The exact concentration of chromic acid will, of course, vary with the concentration of chromic acid in the plating bath itself and also with the amount of water which is used in the tank 4 to remove the plating solution from the articles.

The articles are carried from the fog tank 4 into counterflow rinse tanks 5, 6 and 7 where substantially all of the plating solution which remains on the articles'after they leave the tank 4 is removed. As shown, deionized water is fed to the tank 7 from which it passes over a weir into the tank 6 from which it passes over a weir into the tank 5 and from the bottom of which it is pumped via a pump 11 through a cation exchanger 12. Because of the large amounts of water which are used in the rinse tanks 5, 6, and 7 the solution which is pumped from the tank 5 through the cation exchanger 12 is an extremely dilute solution of the platingsolution, e.g. about to 200 ppm, and any impurities which were carried therefrom by the articles and the conveyor. The solution which is pumped through the cation exchanger 12 thus can have a concentration of chromic acid of less than one-tenth of 1 percent and as it passes through the cation exchanger any cationic contaminants such as positive iron ions are removed and'held on the cation resin contained in the exchanger 12. The solution from which the cations have been removed then flows under the force exerted thereon by the pump 11 through an anion exchanger 14 to remove the anions contained in the solution. The principal ones of these anions will, of course, be the hexavalent chromium ions. The output from the anion exchanger 14 is deionized water from which the cations and anions have been removed by the exchangers l2 and 14 and it is used to feed the counterflow rinse tanks 5, 6, and 7 and the fog nozzles 8 in the tank 4. Any make-up water which is required for the metal recovery tanks 4, 5, 6, and 7 is supplied to the tank 5 from which it passes through the two ion exchangers before being used for rinsing purposes.

During the electroplating process which takes place in the plating tank 3, some of the hexavalent chromium in the chromic acid will be reduced to trivalent chromium. In addition, other metallic impurities may be introduced into the chrome bath by way of the preceding rinse, by the use of auxiliary steel anodes during the chromium plating operation, and by parts which may have dropped ofi the conveyor remaining in the bottom of the plating tank. All of these produce undesirable cations which should be removed from the recovered plating solution before it is returned to the plating bath. If these metallic impurities are not removed, there will be a continual increase of the impurities in the bath which will in time prevent satisfactory plating.

As the rinse water is recirculated through the rinse tanks 4, 5, 6 and 7 and the ion exchangers, the final 20 percent of the plating solution is removed from the article and the anions and cations therein are collected in the exchangers l2 and 14.

Since the rinse solution from the tank 5 contains a very small number of cations relative to the number of chromium anions present, the anion exchanger will become exhausted first and when this occurs the anion exchanger must be regenerated. To accomplish this, the exchangers 12 and 14 are disconnected from the lines leading to and from the rinse tanks and in a duplex installation a similar set of exchangers are connected in circuit with these rinse tanks so that the plating line may continue in operation during regeneration of the exhausted ion exchange resins.

The anion exchanger is preferably regenerated with sodium hydroxide, NaOH, and since all of the sodium in the sodium hydroxide will eventually have to be removed by the cation exchanger, it is important that a minimum amount of sodium hydroxide be used to regenerate the anion resin. In order to accomplish this, the regeneration of the anion exchanger 14 takes place in two steps with the first regenerant flow through the anion resin being a regenerant which has been used once in the preceding regeneration of the resin. This used sodium hydroxide is contained in a tank 16 and is pumped through a valve 17 by a pump 18 through the anion exchanger 14 and into the cation exchanger 12. This regenerant is fed from the cation exchanger'12 into the holding tank 10. As this onceused sodium hydroxide passes through the cation exchanger 12, the sodium ions contained therein will be exchanged for hydrogen ions. Unless, of course, a very large cation exchanger is used, the cation exchanger will not have sufficient capacity to hold all of the sodium ions so that some of these ions will, in an economical system constructed in ac cordance with the present invention, still be present at this time and flow into the holding tank 10.

After the used regenerant has passed through the anion exchange column 14 and through the cation exchange column 12 into the holding tank 10, fresh sodium hydroxide from a tank 20 is pumped by the pump 18 through a valve 21 and through the exchanger 14 and a valve 22 into the tank 16 wherein it is retained until it is to be used in the next succeeding regeneration of the anion exchanger 14. After the used anion regenerant has passed through the exchangers l2 and 14, the cation exchanger 12 is regenerated by pumping sulfuric acid, H 50 from a tank 25 with a pump 26 through the cation exchanger 12. The used cation regenerant may then be treated in the normal manner.

After the cation exchanger 12 has been regenerated, the contents of the holding tank 10, which may contain metal impurities supplied thereto directly from the fog tank 4, is pumped via a pump 28 through the cation exchanger 12 and into a second holding tank 29. Any cationic impurities in the contents of the holding tank are thus removed by the exchanger 12 so that the contents of the holding tank 29 is a purified solution of chromic acid having a concentration of about 24 percent.

When all of the contents of the holding tank 10 have been pumped through the cation exchanger 12 into the holding tank 29, the cation resin is again regenerated in the normal manner by pumping sulfuric acid from the tank 25 through the exchanger 12. The ion exchangers 12 and 14 may now be put back in the line between the inputs to the rinse tanks 4 and 7 and the outlet from the rinse tank 5.

The contents of the holding tank 29 which is a purified and fairly concentrated solution of chromic acid is pumped by a pump 30 into a suitable evaporator 31 before it is returned in concentrated form to the plating tank 3.

The various aspects of the invention described in detail hereinabove are illustrated further by the following specific examples:

EXAMPLE 1 A decorative chrome plating bath is made up with 33 oz./gal. of granular chromium trioxide, 0.33 oz./gal. of sulfate ion and 0.027 oz./gal. of fluoride ion. The sulfate is obtained by the addition of sulfuric acid, and fluoride by the addition of potassium fluoride. In this example a current density of approximately 300 amps per square foot is employed with a conventional rack machine in which the racks are at each of five stations in the chrome plating tank for approximately seconds. The rack contains 10 square feet of surface area to be electroplated resulting in a current flow of approximately 3,000 amps per rack.

With a conventional work piece having a somewhat complex shape, each rack carries out approximately 4 fluid ounces of chromium plating solution when the rack is removed from the bath. At a 90 second indexing time, a total of 40 racks per hour are removed so that fluid ounces of solution are removed from the bath each hour. This results in a drag-out of 1.09 gallons of solution per hour and the loss of 36 ounces of CrO from the plating tank. In addition 0.36 ounces of sulfate and 0.029 ounces of fluoride are dragged out each hour.

Each rack removed from the bath is passed first through a conventional fog rinse tank where 80 percent of the plating solution carried from the bath is washed off using deionized water. The relatively concentrated solution of chromate, sulfate and fluoride ions containing approximately 2 to 4 percent chromic acid is collected in a holding tank and then sent directly through a cation exchange resin to an evaporator.

The balance of the constituents, namely, 7.2 ounces of CrO per hour, 0.072 ounces of S0 and 0.0059 ounces of fluoride per hour are carried with a recirculating flow of 30 gallons per minute of demineralized water through cation and anion ion exchanger and back to the first rinse tank. This very dilute plating solution containing approximately 0.004 percent chromic acid is passed first through the cation exchanger where metallic impurities and none of the basic bath constituents are removed. Then it is passed through the anion exchanger where the chromate, sulfate and fluoride ions are picked up on the anion exchange resin.

The anion exchange column is then regenerated with sodium hydroxide and the chromate, sulfate and fluoride ions are eluded in the sodium form with a small amount of excess sodium hydroxide. This spent regenerate is then passed through the cation exchanger where the sodium is removed and replaced with hydrogen. The chemical balance of the solution can be maintained by small additions of potassium hydroxide or alternatively by passing a small amount of the solution through a potassium form cation resin. When operated in the above manner it is found that the discharge of the evaporator contains exactly the same analysis as the electroplating bath. If the bath becomes more dilute than desired due to drag-in of water from the preceding rinse, the concentration of the discharge from the evaporator can be increasedso that the addition of the evaporated solution to the bath results in the correct concentration.

EXAMPLE 2 In this example, copper is recovered from a plating solution in a similar manner to the example given above for the recovery of chromium. ln a bath containing 28 oz./gal. of copper sulfate, 8.0 oz./gal. of sulfuric acid, 0.0013 oz./gal. of thiourea, 0.0013 oz./gal. of dextrin and 0.0016 oz./gal. of hydrochloric acid, and using the same rack size, shape and plating time of Example 1, 1.09 gal. of copper plating solution are dragged out per hour. This amounts to a drag-out per hour of 30.6 oz. of copper sulfate, 8.7 oz. of sulfuric acid as well as proportionally small amounts of thiourea, dextrin and hydrochloric acid.

Eighty percent of the drag-out solution is recovered in a fog rinse tank and sent directly to the evaporator where it is concentrated up to bath strength without further purification. The other 20 percent of the copper plating solution is recovered in the demineralizer system where the copper is removed by the cation exchanger and the sulfate and chloride are removed by the anion exchanger. The thiourea and dextrin are absorbed on the anion exchanger resin and lost during regeneration so that regular make-up of these materials requires direct additions to the bath.

In this example the copper from the copper sulfate which is removed on the cation exchanger is discharged as copper sulfate when the cation resin is regenerated with sulfuric acid. By careful selection of the regeneratelevel the required excess of sulfuric acid flows directly to the evaporator and 'efiluent from the evaporator is obtained which contains thesame chemical analysis as the original plating bath. Chloride ion loss in the anion exchanger is replaced by the addition of hydrochloric acid to the plating bath.

EXAMPLE 3 in this example a Watts-type nickel bath containing 36 oz./gal. of nickel sulfate, 5 oz./gal. nickel chloride, 4 oz./g'al. boric acid at a pH of 3.5 was treated in a manner similar to the copper plating example given above. In this case, however, since the solution contains both nickel sulfate and nickel chloride, the cation column is regenerated with a mixture of sulfuric acid and hydrochloric acid in the same ratio as the nickel sulfatemickel chloride ratio so as to maintain the chemical balance of the effluent from the cation exchanger during regeneration. During the plating operation the boric acid breaks down and it is necessary for additions of boric acid to be made directly to the bath to maintain the proper chemical balance of the plating solution. The borate from the boric acid is picked up on the anion exchanger and removed from the system in the spent regenerate from the anion exchanger for discharge directly to the sewer.

What is claimed is:

l. A method of recovering H CrO from articles which are wetted with a solution of H CrO comprising the steps of spraying a fine mist of deionized water on said articles to rinse the major portions of said plating solution therefrom,

collecting the solution thus recovered from said articles,

then immersing said articles in flowing deionized water to remove the remainder of said plating solution therefrom,

then treating the water in which said articles have been immersed with a cation resin to remove cation impurities therefrom and with an anion resin to remove CrO ions therefrom, reusing the deionized water which results from the treating of said water with said resins to rinse said articles,

regenerating said anion resin by passing a regenerant therethrough to remove said CrO ions from said anion resin,

passing the regenerant from said anion resin through said cation resin to remove therefrom any cations contained therein,

regenerating said cation resin by passing an acid solution therethrough, then passing said collected solution resulting from said spraying step and the anion regenerant solution which was passed through said cation resin through said cation resin to remove any cations contained therein, and

concentrating by means of evaporation said solution after passage through said cation resin.

2. A method of recovering metal from a plating solution in which articles to be plated are immersed, comprising the steps of first removing the majority of said solution from said articles while maintaining said solution in a concentrated state,

collecting the concentrated solution removed from said articles,

then rinsing said articles with water to remove the remainder of said solution therefrom,

treating said remainder of said solution and rinse water successively with a cation resin and an anion resin and then reusing the resultant liquid for rinsing additional ones of said articles,

regenerating one of said resins by treating it with a regenerant,

treating the regenerant which has passed through said one of said resins with the other of said resins,

treating all of the said collected solution only with said other of said resins, and

combining and concentrating the solutions treated with said other of said resins.-

3. A method according to claim 2 wherein the solution first removed from said articles has a concentration of said plating solution of the order of2 to 4 percent, and g the solution obtained from said rinsing of said articles has a concentration of said plating solution less than about one percent.

4. A method according to claim '3 wherein said plating solution is H CrO 5. A method according to claim 3 wherein said plating solution is nickel.

6. A method according to claim 3 wherein said plating solution is copper.

7. A method according to claim 2 wherein said other of said resins is regenerated between the time said remainder of said solution is treated thereby and the said collection solution is treated thereby.

8. A method of recovering metal from a plating solution in which articles to be plated are immersed, comprising the steps of first removing and collecting the majority of said plating solution from said articles,

then rinsing said articles in water to remove the remainder of said solution therefrom,

treating said remainder of said solution successively with a cation resin and an anion resin and then reusing the resultant water for rinsing additional ones of said articles,

regenerating said anion resin by first treating it with a caustic solution and then passing said caustic solution across said cation resin and combining it with the collected plating solution,

regenerating said cation resin and then treating the combined caustic and collected plating solution with said cation resin, and

then concentrating the combined caustic and collected plating solutions after treatment with said cation resin.

9. The method according to claim 8 further including the step of treating said anion resin with a fresh caustic solution after said first treating step, and thereafter reusing the thus used caustic solution for performing said first treatment in a succeeding anion resin regenerating step. 

2. A method of recovering metal from a plating solution in which articles to be plated are immersed, comprising the steps of first removing the majority of said solution from said articles while maintaining said solution in a concentrated state, collecting the concentrated solution removed from said articles, then rinsing said articles with water to remove the remainder of said solution therefrom, treating said remainder of said solution and rinse water successively with a cation resin and an anion resin and then reusing the resultant liquid for rinsing additional ones of said articles, regenerating one of said resins by treating it with a regenerant, treating the regenerant which has passed through said one of said resins with the other of said resins, treating all of the said collected solution only with said other of said resins, and combining and concentrating the solutions treated with said other of said resins.
 3. A method according to claim 2 wherein the solution first removed from said articles has a concentration of said plating solution of the order of 2 to 4 percent, and the solution obtained from said rinsing of said articles has a concentration of said plating solution less than about one percent.
 4. A method according to claim 3 wherein said plating solution is H2CrO4.
 5. A method according to claim 3 wherein said plating solution is nickel.
 6. A method according to claim 3 wherein said plating solution is copper.
 7. A method according to claim 2 wherein said other of said resins is regenerated between the time said remainder of said solution is treated thereby and the said collection solution is treated thereby.
 8. A method of recovering metal from a plating solution in which articles to be plated are immersed, comprising the steps of first removing and collecting the majority of said plating solution from said articles, then rinsing said articles in water to remove the remainder of said solution therefrom, treating said remainder of said solution successively with a cation resin and an anion resin and then reusing the resultant water for rinsing additional ones of said articles, regenerating said anion resin by first treating it with a caustic solution and then passing said caustic solution across said cation resin and combining it with the collected plating solution, regenerating said cation resin and then treating the combined caustic and collected plating solution with said cation resin, and then concentrating the combined caustic and collected plating solutions after treatment with said cation resin.
 9. The method according to claim 8 further including the step of treating said anion resin with a fresh caustic solution after said first treating step, and thereafter reusing the thus used caustic solution for performing said first treatment in a succeeding anion resin regenerating step. 